We borrow mainly from [1]}, Ch. 9 (and see also the authors's book in progress [2]}). One may take generators for the lattice which depend locally analytically on \(\lambda \) , but have monodromy as we move \(\lambda \)  in \({C}-\lbrace 0,1\rbrace \) . In the region \(\max (|\lambda |,|1-\lambda |)<1\) , we may pick the periods as given by
\(\omega _1(\lambda )=i\pi F({1\over 2},{1\over 2},1,1-\lambda ),\qquad \omega _2(\lambda )=\pi F({1\over 2},{1\over 2},1,\lambda ),\) 
